This invention relates to an electrosurgical generator, and more specifically to an electrosurgical generator which selectively generates a variety of coagulate signals and cutting signals.
Past electrosurgical generators normally produced a variety of signals and have controls to adjust signal strength and other parameters of operation. One problem with past electrosurgical generators has been that the multiplicity of controls impaired the treating physician's ability to switch rapidly from one signal mode to another, a particularly crucial problem when medical exigencies require rapid response. Since such controls are most useful when placed within easy reach of operating personnel, isolation from shock hazard is very important, not only for the patient, but also for the physician. Past generators have typically used only a single isolation transformer with the side taps coupled through blocking capacitors to the output terminal. This isolation scheme has often proved inadequate to eliminate the danger of electric shock. For a discussion of the prior art of isolation, see the U.S. Pat. No. 4,094,320 assigned to Valleylab, Inc.
Furthermore, past electrosurgical generators have produced a simultaneous cutting and coagulating effect, known in the art as a blend signal, by literally blending a cut signal and a coagulate signal. Since significantly different signal levels are required to produce comparable levels of effectiveness between these two signals, past generators have included complex hardware to accomplish an effective literal blending. See, for example, the U.S. Pat. No. 4,154,240.
Incisions created by electrosurgical generators are based on the creation of an ionization path between the closely-spaced electrodes of the electrosurgical scalpel. Past generators have normally utilized high power output levels to maintain an active ionization path, which not only required a massive power supply and generating hardware, but also dissipated waste heat along the incision, and disrupted tissue unnecessarily. A typical prior art electrosurgical incision of the skin would therefore cause a continuous explosive sputtering of the fat layer directly underneath the skin, and the skin incision would heal slowly to produce substantial scar tissue. Users of prior art electrosurgical generators would typically make an initial incision through the skin and fat layer with the traditional knife scalpel in order to avoid this problem.
Some prior art generators have featured a constant-current output amplifier in order to produce a uniform electrosurgical effect over a fairly broad range of tissue impedance. See U.S. Pat. No. 3,601,126 for an output feedback system to maintain constant output levels. Where differing signal frequencies were used as the basis for different generator output modes, the change in frequency would change the output impedance of the amplifier. In this regard see U.S. Pat. No. 3,699,967, assigned to Valleylab, Inc. Thus, past generators with constant-current output amplifiers were in fact limited to a fairly narrow range of tissue types and incision techniques.